In the course of treating and preparing subterranean wells for production, a well packer or bridge plug is run into the well on a work string or a production tubing. The purpose of the packer or bridge plug is to provide isolation between zones of the wellbore. For example, the packer or bridge plug can be used to seal the annulus between the outside of the production tubing and the inside of the well casing to block movement of fluids through the annulus past the packer or bridge plug location. The packer or bridge plug is typically provided with anchor slips having opposed camming surfaces which cooperate with complementary opposed wedging surfaces; whereby the anchor slips are radially extendible into gripping engagement against the well casing bore in response to relative axial movement of the wedging surfaces.
The packer or bridge plug also carries annular seal elements which are expandable radially into sealing engagement against the bore of the well casing. Longitudinal movement of the packer components which set the anchor slips and the sealing elements may be produced either hydraulically or mechanically.
After the packer or bridge plug has been set and sealed against the well casing bore, it should maintain sealing engagement upon removal of the hydraulic or mechanical setting force. Moreover, it is essential that the packer or bridge plug remain locked in its set and sealed configuration while withstanding hydraulic pressure applied externally or internally from the formation and or manipulation of the tubing string and service tools without unsetting the packer or bridge plug or without interrupting the seal. This is made more difficult in deep wells in which the packer or bridge plug and its components are subjected to high downhole temperatures, for example temperatures up to and exceeding 400° F., and high downhole pressures, for example, 5,000 pounds per square inch (“psi”).
One common problem with packers and bridge plugs is the release of their slip assemblies prematurely. In passing through restrictions in the wellbore or when encountering debris, the slip assembly can be released thereby prematurely engaging the casing.